As the United States grows and evolves, innovators fix many of our modern problems. Evolutions in medicine extend lives for millions. Technology enriches us and enables communication like never before. Yet, traffic remains utterly unsolved. While we have come up with new ideas that improve our ability to circumvent traffic, such as Waze or Google Maps, at best, these solutions spread traffic out rather than eliminating it. Traffic costs money, time, and even health due to the stress of waiting in traffic and understanding the consequences of being late. And yet, we still rely on roads to get to where we need to go, same as everyone else. While underground subways offer an alternative in urban environments like Washington, DC, that option is expensive and thus less practical out in the suburbs. This is why the scientific examination of what causes traffic is so critical.
By exploring why we have traffic, we can consider what solutions exist. Moreover, this query is among the most common questions people wonder, given just how prevalent it is if you live anywhere near a metropolitan area. Moreover, traffic is directly related to our law practice. At Gelb & Gelb, we have represented over 10,000 clients, a large majority of whom are due to car accidents. If car accidents are not the cause of much of the traffic, then traffic leads to car accidents. Accordingly, they are intertwined and thus highly relevant to our practice of law. We will share our unique insight into the car accident portion of this discussion, while also sharing research that answers the question of why traffic exists.
The Science of Traffic Shockwaves
A shockwave occurs when one driver suddenly slows down, forcing the next driver to brake, and so on, until the slowdown ripples backward through hundreds of cars. What begins as a single moment of hesitation can cause miles of gridlock without any visible obstacle ahead. These are invisible waves that illustrate how sensitive traffic flow truly is. If you are in heavy traffic that seems to dissipate suddenly and for no reason at all, you were probably affected by a shockwave. This is also known as a phantom traffic jam. These traffic jams are more scientific than you may expect. In fact, mathematical formulas are ingrained in the design of roads and traffic, accounting for these traffic shockwaves. According to researchers at MIT, there is a stabilizing traffic pressure due to preventive driving.
On the other hand, there is a destabilizing effect from drivers slowing down when vehicle density is higher, as well as a delay in drivers’ adjustment to new conditions. The adjustment time is inversely related to the “aggressiveness” of the drivers. They act very similarly to how an actual shockwave acts under the laws of physics. Studies have also shown that tailgating makes this worse. If there is sufficient space between vehicles, there may be no need to brake when the car in front of you brakes.
Moreover, by not tailgating, you avoid the risk of crashing and being at fault. Besides a car braking being a culprit, another reason why a shockwave may occur, albeit to a lesser degree, is due to a lane change. Just as a car may need to slow down if the car in front of it slows, cars may also need to slow down if a vehicle merges in front of them. Then, you are left with the same traffic shockwaves.
Common Causes of Traffic Congestion
Traffic jams always have an explanation. You may wonder why there always appears to be traffic in one intersection or on one road. This must surely be a design failure. But it may also be due to the time of day, when schools and churches are letting people out, or if there is a sports arena that often hosts special events. Below, we consider why traffic most often slows to a crawl.
Car Accidents and Road Incidents
Care accidents and other road incidents are a surefire way to create traffic. Even minor car accidents can disrupt traffic for miles. When a collision occurs between two or more vehicles, several things happen. First, the vehicles in the accident stop moving. In more serious accidents, they may flip over or become inoperable, meaning a tow truck will eventually arrive to move the car out of the lane. But until the drivers in the accident move their cars, traffic comes to a complete halt, at least in those lanes. Then, once they move to the side of the road, if there is a safe emergency lane, it will attract onlookers, or “rubber necks,” for as long as they are there. Moreover, emergency vehicles will enter the flow of traffic, further disrupting the flow of traffic for everyone else.
These reactions trigger chain slowdowns. Some refer to these slowdowns as “shock waves,” as they can persist long after the vehicles leave the scene. In really bad accidents, glass may shatter and fly across the road. Perhaps a bumper was struck so hard that it fell off a vehicle and into the roadway. Unfortunately, these become obstacles that other drivers have to avoid. This may require merging into other lanes even after the cars involved in the accident have moved. While a major inconvenience and surely a cause of road congestion, driving by an accident can serve as a stark reminder of how inconvenient it is for everyone else and how serious injuries can be for those involved.
Construction and Road Work
When there is construction or roadwork on a highway or local street, several things happen. First, local laws generally implement harsher penalties for speeding. Thus, drivers rightly slow down. They understand that there are pedestrians around high-speed areas on the interstates. This presents a serious threat, where even a minor mistake could have disastrous consequences. Accordingly, many right-minded individuals slow down. Consequently, breaking leads to traffic shockwaves and a bit of traffic. But of course, this by itself does not create massive standstills. Lane closures, detours, and uneven road surfaces slow travel times. It also confuses drivers, who are unsure of how their wheels will react to the surface. But real traffic problems arise when road workers have to stop traffic entirely in one direction.
This happens most often on local roads. You may imagine one road worker in one direction holding a “stop” sign, while the other road worker in the opposite direction holds a “slow” sign. When this happens, it is best to avoid the road entirely and use an alternative route. Otherwise, you may be stuck in traffic for far longer than expected. Especially during peak travel times, like rush hour, this traffic can back up into intersections and even disrupt traffic flow in different directions and on different streets. Unfortunately, this effect can quickly expand in all directions and be felt miles away. This is one reason why you may unexpectedly have traffic on a street and not even see a reason why this may have occurred.
Rush Hour Traffic
Rush hour traffic is reliably dreadful. This cause of traffic is one of the most predictable causes of traffic. You can predict when, where, and why traffic will occur merely by looking at zoning patterns in a given region. As commuters head to and from work during the same time windows each day, more people enter the roadway than the infrastructure can efficiently handle. While traffic light cycles are timed according to what urban planners think will most effectively circulate traffic, it never feels like enough. Or worse, even though your light is green, there is nowhere to go once you enter through the intersection. The result, among other things, is several shockwaves that build on each other with no place to release as more cars keep coming.
Then, especially in urban environments, if FedEx or USPS is parked in a lane to drop off packages at the end of the day, it has a dramatic effect on already busy roads. Not only is a lane out of commission in a high-traffic area, but merging everyone out of that lane can cause delays of up to 10 minutes for a singular issue. Perhaps the largest issue with rush-hour traffic is twofold. First, there are more cars on the road. This means that there are more opportunities for traffic shockwaves to occur. Second, there is nowhere for the traffic shockwave to escape. This leads to the single most common cause of traffic. And while it is not necessarily the worst cause of traffic, it is consistently tiresome, leading to congestion fatigue.
Weather Conditions
Weather conditions can amplify the effects of the other conditions we list here. For example, if adverse weather conditions occur during rush hour or roadwork, traffic is exacerbated. Rain, snow, fog, and ice can all contribute to slowing traffic. For example, in fog, it is prudent to slow down as you cannot see as far in front of you. This braking causes traffic shockwaves behind you as the drivers behind you then have to brake. Similarly, rain also reduces visibility. While some drivers will still drive fast through the rain, this only increases the chances of a crash, leading to more traffic. If you are a prudent driver in rain or fog, you slow down to avoid these risks. However, slowing down does inherently increase traffic.
Snow and ice can also reduce visibility, but for different reasons. Of course, both hazards present significant risks to drivers. But snow can also be tricky because it is hard for drivers to know where lanes start and end. Thus, it is easier to drift into someone else’s lane. Furthermore, when a driver is on ice, braking is next to impossible. Accordingly, drivers should proceed with extreme caution when traveling on ice. While that is the correct step to take, the slower speeds do create traffic. The last weather condition to consider is when the weather, even including rain, turns to flooding that renders a lane unusable. When a lane is shut down due to flooding, there is less room for traffic to flow, and traffic shockwaves will occur due to consistent merging.
Lane Merging and Bottlenecks
Few things cause as much frustration as a sudden lane drop or poorly designed merge. Even reading this now, you can probably imagine a bottleneck that always has traffic, regardless of the time of day. A bottleneck occurs when traffic flow is restricted by a physical or functional limitation on the road, such as a lane closure, a narrowing section of highway, or an on-ramp feeding into heavy traffic. When thinking of a bottleneck, it may help to literally imagine a plastic water bottle. The flow of water (or traffic) must slow to make it through the neck of the bottle. At a bottleneck, it is most often the merging that slows everyone down. This sends traffic shockwaves back to the people on the main highway. Moreover, the people entering the main highway must slow down to wait for those ahead in their lane to merge.
Unfortunately, if there is a poorly designed merge section, this can only make matters worse. When this happens, the lane entering the main road will move even more slowly. As those merges are slower, the traffic shockwaves will be more significant. Examples may include short acceleration lanes, unclear signage, or sudden lane drops, which give drivers little time to adjust. With little time to adjust, drivers move more slowly. Moreover, these last-second maneuvers can lead to collisions. This is especially true when a driver does not realize that there is a short merge lane. Or, worse than that, you read a sign that says “no merge area”, but it is too late. As personal injury lawyers, we are familiar with the bottlenecks in Washington, DC, Maryland, and South Carolina, which consequently see the most accidents in their respective states.
Inefficient Traffic Signals and Intersections
Traffic lights should be synchronized so that the vehicles approaching the light do not have to wait. In an ideal world, they are timed so that the light turns green just in time for the vehicles from the previous intersection to continue through. Obviously, this does not always happen. Another interesting and useful point is that a stoplight is generally timed based on the speed limit. The duration of the yellow light should be equal to the speed limit divided by 10. For example, in a 55-mile-per-hour zone, the yellow light should remain on for 5.5 seconds. In a 35-mile-per-hour zone, the yellow light should remain on for 3.5 seconds. When traffic lights behave efficiently, there is nothing more that can reasonably be done.
However, when your lane is full, and traffic going the other direction is green but has no one traveling through the intersection, that is an inefficient traffic signal. One solution is adaptive signal control technology. Adaptive signal control technology adjusts the timing of red, yellow, and green lights to accommodate changing traffic patterns and ease traffic congestion. At the least, this should stop instances where a driver is fuming at a red light, seeing that no one is driving in the other direction. According to the Department of Transportation, outdated traffic signals account for more than 10 percent of all traffic delay and congestion on major routes alone. According to the Texas Transportation Institute, the cost of traffic congestion is $87.2 billion in wasted fuel and lost productivity. That translates to $750 per traveler.
Special Events and High-Volume Areas
Concerts, sporting events, parades, and festivals temporarily overwhelm surrounding road networks. This is especially true both before an event starts and when an event is ending. When this happens, roads that are not otherwise designed for that many people become overwhelmed. This creates backups that spill onto highways and nearby neighborhoods. This happens because people suddenly leave at the exact same time. However, another reason is that some roads may be shut down to allow pedestrians to enter and exit on their way to public transportation or even to nearby garages. When a road is inaccessible, it overwhelms the available roads even more. Of course, this has a ripple effect that spreads to other roads and intersections.
The good news here is that there are ways to mitigate this type of traffic. City planners and event organizers often work together to minimize these disruptions through temporary traffic management plans. This often involves crossing guards and traffic cops directing traffic. It is actually a highly effective way to support traffic flow. Similar to adaptive signal control technology, a human crossing guard can detect which lanes need more help. Perhaps the only downside is that the communication between crossing guards in different intersections may not be as effective as automation. If you are driving near an arena, check event schedules and plan alternate routes as necessary.
The Role of Human Behavior
As you can see, there are several common causes that are generally outside of human behavior. However, there are plenty of things that people do that contribute to traffic. Off the top of your head, you probably think of car accidents. And that is one clearly caused by humans that certainly contributes to much of the traffic on the road when traffic is at its worst. But if we are to nitpick a bit, there are other causes besides accidents that humans contribute to. In fact, the way drivers react, accelerate, brake, and merge can make the difference between smooth movement and complete gridlock. Research in traffic flow theory consistently shows that human error and impatience account for a large portion of everyday congestion. As we touched on above, aggressive driving tactics such as tailgating, but even quick merges in and out of lanes, create more traffic shockwaves.
While an isolated incident may not create standstill traffic, when this happens at scale, the shockwaves do not stop, and traffic happens. Other phenomena that create traffic include distractions. This is a broad category of human behavior. For example, if a driver is on their phone, they may be slow to accelerate when traffic is moving ahead of them. Again, at scale, this can cause people to miss lights and back-up traffic. Another example within the category of distraction is rubbernecking. This is the tendency to slow down to look at accidents or roadside activity. The name comes from turning your neck to look at the activity. Drivers who divert their attention, even briefly, reduce lane efficiency and increase the risk of secondary collisions.
How Road Design Impacts Traffic
A major factor in how road design impacts traffic is the capacity of the road. This is a feature of roads that city planners have to consider. Many roads and highways in the United States were built decades ago, when vehicle ownership and commuting patterns were vastly different. Thus, city planners have to combat this by expanding roadways and adding lanes. Of course, this is not always possible – particularly in downtown, urban environments. Especially when you consider the growth rate of a given city, it makes sense why traffic would be so bad. Additionally, sharp turns, blind spots, or sudden elevation changes can cause drivers to reduce speed unexpectedly, creating slowdowns. While this may not lead to standstill traffic, it can certainly cause more congestion as there will likely be consistent traffic shockwaves in that location.
Another road design that directly slows down traffic but makes the city more walkable is the use of crosswalks. A crosswalk in the middle of a busy street can cause all three lanes in each direction to halt for at least 15 seconds. To be clear, crosswalks are a great thing because they keep pedestrians safer. However, city planners know to be careful in how many they implement. Sometimes, it is best to make pedestrians walk a block past where they want to go to avoid having too many crosswalks. At the same time, if the crosswalk is too far away, a pedestrian may walk past where they want to go, jaywalk, and cause an accident.
Other ways road design impacts traffic include narrower streets, parallel parking spaces, and unenforced jaywalking. Each of these can create shockwaves. Any susceptibility done at scale can wreak havoc on traffic.
Technology and the Future of Traffic Management
Some cities have seen historic growth. In 2024, some cities in the United States grew as much as 30% in a single year. Even cities like New York City and Washington, DC, grew by about 1% in population in a single year. While 1% is not quite as much as 30%, it is enough that if it continues to compound, it will quickly overwhelm its infrastructure and create problems for traffic. This is why a city must innovate. We already mentioned adaptive signal control technology. Another technology that could aid traffic flow is connected and autonomous vehicles (CAVs). These are vehicles that communicate with each other, likely through Bluetooth. This helps to avoid nearly all of the traffic shockwaves from a brake or a merge. No longer is one car braking, then another, then another. Instead, all cars brake and accelerate at precisely the same time.
These cars could also communicate with each other about upcoming hazards, potentially preventing accidents and saving lives. Of course, companies like Waymo and Tesla are working at a high clip to be the first to fully implement this. But even then, for it to work best, it will need to be able to communicate with all vehicles on the road. This ultimately will require legislation to get people to give up their autonomy behind the wheel. Looking away from the drivers and to the traffic systems we have in place, artificial intelligence, machine learning, and smart infrastructure can all aid traffic. This may include digital road signs, highway sensors, and new transit systems. Newer tactics we see also include congestion pricing, which acts as a supply and demand model, keeping out masses of vehicles from certain roads.
How Understanding Traffic Can Prevent Accidents
Of course, understanding how traffic works and its causes can help you avoid getting into traffic in the first place. But how does this help you avoid accidents? Driving is relatively easy when you are on a highway, have plenty of space in front of you and behind you, and do not have to merge out for hours. In that instance, the only thing you have to do is stay in your lane and not go too fast. But when you are in traffic, every slowdown, bottleneck, and traffic wave reflects countless small decisions made by individual drivers. These present far more chances to get into accidents than when you are just driving straight with no traffic. So, what can you do to avoid accidents while in traffic? First, recognize that you are entering a bottleneck or merge zone. These are higher-risk areas.
Thus, you should stay alert, maintain a safe distance from the car in front of you, and be aware that drivers may try to cut in front of you in line, which is okay. But how else does understanding traffic prevent accidents? It should reduce the number of sudden reactions you must take from behind the wheel. It promotes safer following distances. Understanding traffic also allows for lower stress, better anticipation, more predictable driving, and potentially better road design and policy, depending on the audience.
Contact Gelb & Gelb Today
Gelb & Gelb is a personal injury law firm serving Washington, DC, Maryland, and South Carolina. We have practiced personal injury law and handled car accident cases for over 70 years, representing over 10,000 clients for their injuries. In this time, we have spoken to and worked on nearly every conceivable type of car accident. We have an acute understanding of what goes on in the minds of people behind the wheel. Much of the time, it is distraction, boredom, and lack of awareness that contribute to the accident occurring. During cross-examination, we often ask if the adverse driver had a specific destination and if traffic was causing delays to their arrival at this important event.
These details matter because they reveal that accidents rarely occur by chance. Accidents are the result of decisions, pressures, and habits that lead to behavior behind the wheel. If you are in a motor vehicle accident, whether in a car, truck, or as a pedestrian, we may be able to help. We represent nearly all victims who are injured due to another person’s negligence. Call us today at (202) 331-7227. Our consultations are always free.
